JPS64530B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for removing negative frictional force that tends to pull in cast-in-place piles such as foundation piles of buildings due to ground subsidence.

Conventional Technology Foundation piles constructed on soft ground such as reclaimed land are subject to negative frictional force that tries to pull the foundation piles together as the ground sinks due to the consolidation action of the ground, causing buildings, etc. This caused unexpected subsidence in the foundations of buildings, which caused the buildings to tilt and crack, and even caused the piles to break.

Conventionally, in such areas of subsidence, double steel pipes were used, or steel pipes were coated with a friction cutting material such as asphalt beforehand and ready-made piles were driven into them. Instead, as shown in Fig. 2, a plurality of plates 12 with asphalt 11 etc. attached are attached to the outer periphery of a reinforcing bar cage 13 with wires 14 and built into the excavated hole 15, and the plates 12 are placed under the pressure of the poured concrete. Therefore, the only known method is to form a concrete pile by pressing a plurality of plates 12 against the wall of an excavated hole 15 (see Japanese Patent Publication No. 58495/1983).

Problems to be Solved by the Invention In conventional technology, with ready-made piles, it is possible to apply a frictional cutting material such as asphalt to the pile, but with cast-in-place piles, it is not possible to apply a frictional cutting material to the pile in advance. However, in the method of using plates of cast-in-place piles, it is necessary to prepare a plate to which friction cutting material is attached and attach it movably to the reinforcing cage, and since the plate is buried together with the pile, a large number of plates are required. Furthermore, since the plate is attached to a reinforcing bar cage, the diameter of the reinforcing bar cage must be made smaller than conventional ones, which not only lacks strength against bending and shearing, but also damages the plate and the wall of the borehole. There was a risk that concrete would enter the gap between the two and prevent the frictional force from cutting.

In view of the above points, the present invention aims to provide a simple and reliably effective method for removing negative frictional force using cast-in-place piles that does not require plate materials or the like.

Means for Solving the Problems The means of the present invention for solving the above problems is to construct cast-in-place concrete piles in the ground,
After the concrete hardens, a steel pipe with an injection pipe that has a larger diameter than the concrete pile is inserted into the concrete pile, and then the steel pipe with the injection pipe is pulled up while injecting lubricant into the ground from the tip of the injection pipe. This method consists of a method for removing negative frictional force from cast-in-place piles by forming a permeable layer of lubricant around the concrete pile.

Embodiment An embodiment of the present invention will be described with reference to the drawings.

To explain the construction status with respect to Figures 1a to 1e, Figure 1a shows the state in which cast-in-place concrete piles 2 have been constructed in the ground 1 and the concrete has solidified, and Figure 1b shows the state in which the cast-in-place concrete piles 2 are hardened. is the third steel pipe
As shown in the figure, injection pipes 4 are attached to the peripheral wall of the steel pipe at appropriate intervals. A steel pipe 3 with an injection pipe 4 having a diameter larger than that of the concrete pile 2 and having a gap between it and the concrete pile 2 is inserted from above the concrete pile 2 to a predetermined depth using a water jet or a vibro hammer.
Next, open the valve 5 of the injection tube 4 and insert the tip 6 of the injection tube 4.
The steel pipe 3 is pulled up while injecting a lubricant 7 such as grease, asphalt, or paraffin into the ground 1 (see figure c). When the steel pipe 3 with the injection pipe 4 is completely pulled up, an annular layer 8 in which the lubricant 7 has permeated is formed in the ground 1 around the concrete pile 2 (FIG. d). When the ground 1 sinks in this state, the frictional force between the concrete pile 2, the annular layer 8 surrounding it, and the surrounding ground 1 is cut off by the annular layer 8 penetrated by the lubricant 7. Therefore, the negative frictional force from the surrounding ground 1 does not act on the concrete pile 2, and only the ground 1 sinks, allowing the concrete pile 2 to maintain its original state when it was cast (see e in the same figure).

Effects of the Invention Since this invention uses the above means, (1)
Because it does not use double steel pipes like ready-made piles, it eliminates the need for an outer steel pipe that is heavy and bulky, making it easy to handle and reducing the cost of steel pipes.(2) The steel pipes are coated with asphalt or other friction cutting material in advance (3) Unlike conventional cast-in-place piles, plates coated with friction cutting material are not used, so there is no need to apply friction cutting material, and the work is easy. It is economical because it saves time, (4) the negative frictional force removal effect is reliable because there is no uncertainty in cutting the frictional force unlike in the case where the plate material is used, and (5) the injection pipe is included. The work is easy as all you have to do is inject the lubricant from the steel pipe and pull it up, and (6) it is economical because the lubricant layer can be formed only in the necessary areas by appropriately selecting the depth of the steel pipe. It is.

[Brief explanation of the drawing]

Figures 1 and 3 show one embodiment of the present invention, and Figures 1a to 3e are explanatory diagrams showing the construction state of cast-in-place concrete piles;
The figure is a cutaway plan view showing a conventional cast-in-place concrete pile, and FIG. 3 is an enlarged cutaway plan view of a concrete pile fitted with a steel pipe with an injection pipe. 1...Ground, 2...Cast-in-place concrete pile, 3...
Steel pipe, 4... Injection pipe, 6... Tip, 7... Lubricant, 8...
permeable layer.

Claims (1)

[Claims] 1. After constructing a cast-in-place concrete pile 2 in the ground 1 and solidifying the concrete, a steel pipe 3 with an injection pipe 4 having a larger diameter than the concrete pile 2 is inserted into the concrete pile 2, and then the injection pipe 4 is inserted into the concrete pile 2. The negative impact of the cast-in-place pile is such that a permeation layer 8 of the lubricant 7 is formed around the concrete pile 2 by pulling up the steel pipe 3 with the injection pipe 4 while injecting the lubricant 7 into the ground 1 from the tip 6 of the concrete pile. Frictional force removal method.